1. Field of the Invention
The present invention relates to a chemically amplified photoresist composition that is excellent in transparency to light with wavelengths in the deep ultraviolet region (deep UV light) such as KrF or ArF laser light, and exhibits high sensitivity and definition, to a novel copolymer that is suitable for the preparation of the photoresist composition, and to a process for the formation of a resist pattern with a high aspect ratio. Specifically, the present invention relates to a chemically amplified photoresist composition that is suitable for a process for the formation of a resist pattern with a high aspect ratio using a silylation agent, and to a process for the formation of a resist pattern with a high aspect ratio.
2. Description of the Related Art
To form an ultrafine resist pattern of not more than 0.35 μm, specifically of not more than 0.25 μm, a variety of highly sensitive photoresist compositions having satisfactory transparency to deep UV light such as KrF or ArF laser light have been reported.
Among them, “chemically amplified” photoresist compositions containing a substance carrying an acid-decomposable group, and a photosensitive acid generator are predominant. However, demands have been made to further improve the sensitivity and definition of these chemically amplified photoresist compositions.
Additionally, the use of this type of photoresist compositions alone cannot significantly form a resist pattern with a good shape, especially a hole-type resist pattern with a high aspect ratio and a good shape. As a possible solution to this problem, a technique has been reported in which a second film or coating composed of a silylation agent is formed on the surface of a resist pattern, and using this second film, a resist pattern with a high aspect ratio is formed.
This technique using a silylation agent is reported, for example, in Microelectronic Engineering 11 (1990) 531-534 (Reference 1), and is performed substantially in the following manner.
Initially, a resist film (bottom resist) is formed on a substrate, and this bottom resist is resistant to etching treatment for the substrate. Another resist film is then formed on the bottom resist, using a photoresist composition containing, for example, a polymer having a repeating unit represented by Formula (V) below, and the formed resist film is selectively patterned by exposure and developing to thereby form a resist pattern.
Next, a solution of, for example, a compound represented by Formula (VIII) below (silylation agent) is applied onto the resist pattern and is then rinsed to thereby form a silylation coating on the resist pattern, and the resulting silylation coating is resistant to corrosion induced by oxygen plasma etching.
The underlayer bottom resist is removed by etching using, as a mask, the resist pattern carrying the silylation coating to thereby form a resist pattern with a high aspect ratio. 
Such photoresist compositions that can be applied to this process comprising the above operations must essentially react with a silylation agent to form a silylation coating and must have high sensitivity and definition.
Japanese Patent Laid-Open No. 5-11450 (Reference 2) discloses, as the aforementioned photoresist compositions, a photoresist composition containing a polymer and a photosensitive acid generator, which polymer comprises a (meth)acrylic tert-butyl ester group and a maleic anhydride functional group, and a photoresist composition containing a polymer and a photosensitive acid generator, which polymer comprises a (meth)acrylic tert-butyl ester group, a maleic anhydride functional group, and an allyltrimethylsilane group.
These compositions have satisfactory transparency to deep UV light and have high sensitivity, but their definition must be further improved.
Japanese Patent Laid-Open No. 11-212265 (Reference 3) discloses a photoresist composition comprising a polymer and a photosensitive acid generator, which polymer has a repeating unit represented by Formula (III) and a repeating unit represented by Formula (VII): wherein R1 is a hydrogen atom or a methyl group; and R2 is an alkyl group having from 1 to 4 carbon atoms.
Even this composition must be further improved in sensitivity and definition.
Additionally, when this composition is applied to the process using a silylation agent, it cannot significantly react with the silylation agent to thereby fail to form a silylation coating, and a hole pattern with a high aspect ratio cannot be significantly obtained.